This chapter examines the dynamics of consumer–resource interaction, one of the fundamental building blocks of food webs. In particular, it considers how consumer–resource systems that are ...
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This chapter examines the dynamics of consumer–resource interaction, one of the fundamental building blocks of food webs. In particular, it considers how consumer–resource systems that are nonexcitable and excitable respond to changes in interaction strength. The chapter begins with a discussion of two classes of interaction-strength metrics: the first focuses on instantaneous rates of change in one species with respect to another species; the second follows the longer-term influence of the removal of (or change in) one species on the density of another focal species. Continuous consumer–resource models are then described, after which two underlying mechanisms that are behind the stabilization of consumer–resource interactions are analyzed. The chapter concludes with a review of microcosm experiments and empirical data that show consistency with the proposed consumer–resource theory.Less

Consumer-Resource Dynamics: Building Consumptive Food Webs

Kevin S. McCann

Published in print: 2011-12-11

This chapter examines the dynamics of consumer–resource interaction, one of the fundamental building blocks of food webs. In particular, it considers how consumer–resource systems that are nonexcitable and excitable respond to changes in interaction strength. The chapter begins with a discussion of two classes of interaction-strength metrics: the first focuses on instantaneous rates of change in one species with respect to another species; the second follows the longer-term influence of the removal of (or change in) one species on the density of another focal species. Continuous consumer–resource models are then described, after which two underlying mechanisms that are behind the stabilization of consumer–resource interactions are analyzed. The chapter concludes with a review of microcosm experiments and empirical data that show consistency with the proposed consumer–resource theory.

This chapter focuses on consumer-resource dynamics in systems where consumers of different sizes compete for a shared resource. It considers the implications of three important aspects of consumer ...
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This chapter focuses on consumer-resource dynamics in systems where consumers of different sizes compete for a shared resource. It considers the implications of three important aspects of consumer life history: the explicit handling of a juvenile period leading to a delay between the time when an individual is born to when it starts to reproduce; the rate by which individual ecological processes scale with body size; and whether the rate by which the individual grows is dependent on food density or not. The chapter examines the effects of different resource growth dynamics to illustrate the fundamental differences between population cycles driven by interactions between individuals of different sizes, and classical predator–prey cycles driven by interactions between the consumer and the resource, also referred to as paradox of enrichment cycles. It also discusses experiments with the model organism, the cladoceran zooplankton Daphnia, to elucidate our current understanding of cycles driven by cohort interactions in this organism.Less

Dynamics of Consumer-Resource Systems

André M. de RoosLennart Persson

Published in print: 2013-01-15

This chapter focuses on consumer-resource dynamics in systems where consumers of different sizes compete for a shared resource. It considers the implications of three important aspects of consumer life history: the explicit handling of a juvenile period leading to a delay between the time when an individual is born to when it starts to reproduce; the rate by which individual ecological processes scale with body size; and whether the rate by which the individual grows is dependent on food density or not. The chapter examines the effects of different resource growth dynamics to illustrate the fundamental differences between population cycles driven by interactions between individuals of different sizes, and classical predator–prey cycles driven by interactions between the consumer and the resource, also referred to as paradox of enrichment cycles. It also discusses experiments with the model organism, the cladoceran zooplankton Daphnia, to elucidate our current understanding of cycles driven by cohort interactions in this organism.

This chapter examines the influence of biological lags on consumer–resource dynamics, with particular emphasis on how consumer–resource cycles, or the lack thereof, interact with population level ...
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This chapter examines the influence of biological lags on consumer–resource dynamics, with particular emphasis on how consumer–resource cycles, or the lack thereof, interact with population level dynamical phenomena. It first considers discrete consumer–resource interactions before discussing the dynamics of stage-structured consumer–resource interactions. It then explains how stage structure promotes the possibility of alternative stable states and changes consumer–resource interaction strength. It also shows how a change in population structure affects food web interactions and/or the strengths of food webs. Finally, it reviews empirical results that show how stage structure and food web interaction influence ecological stability. The chapter argues that weak and inherently stable consumer–resource interactions can mute a potentially unstable population level phenomenon, and that a dynamically decoupled stable stage class can strongly stabilize other stages and the consumer–resource interaction.Less

Lagged Consumer-Resource Dynamics

Kevin S. McCann

Published in print: 2011-12-11

This chapter examines the influence of biological lags on consumer–resource dynamics, with particular emphasis on how consumer–resource cycles, or the lack thereof, interact with population level dynamical phenomena. It first considers discrete consumer–resource interactions before discussing the dynamics of stage-structured consumer–resource interactions. It then explains how stage structure promotes the possibility of alternative stable states and changes consumer–resource interaction strength. It also shows how a change in population structure affects food web interactions and/or the strengths of food webs. Finally, it reviews empirical results that show how stage structure and food web interaction influence ecological stability. The chapter argues that weak and inherently stable consumer–resource interactions can mute a potentially unstable population level phenomenon, and that a dynamically decoupled stable stage class can strongly stabilize other stages and the consumer–resource interaction.

This chapter extends the consumer–resource theory to include simple but common three-species modules behind the construction of whole food webs, with particular emphasis on food chains and omnivory. ...
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This chapter extends the consumer–resource theory to include simple but common three-species modules behind the construction of whole food webs, with particular emphasis on food chains and omnivory. It first considers some common simple modular food web structures and whether the dynamics of subsystems can be seen using the framework laid out in previous chapters. Specifically, it asks when common food web structure increases or weakens the relative interaction strengths and/or when a food web structure modifies flux between consumers and resources in a density-dependent manner such that the food web tends to increase flux rates in some situations and decrease the coupling in other situations. The chapter also explores how stage structure can influence food chain stability before concluding with a review of empirical evidence on the dynamical implications of omnivory for food webs.Less

Food Chains and Omnivory

Kevin S. McCann

Published in print: 2011-12-11

This chapter extends the consumer–resource theory to include simple but common three-species modules behind the construction of whole food webs, with particular emphasis on food chains and omnivory. It first considers some common simple modular food web structures and whether the dynamics of subsystems can be seen using the framework laid out in previous chapters. Specifically, it asks when common food web structure increases or weakens the relative interaction strengths and/or when a food web structure modifies flux between consumers and resources in a density-dependent manner such that the food web tends to increase flux rates in some situations and decrease the coupling in other situations. The chapter also explores how stage structure can influence food chain stability before concluding with a review of empirical evidence on the dynamical implications of omnivory for food webs.

This chapter explains the use of modular or motif-based theory to interpret the dynamics of whole food webs. According to Robert Holt, modules are “as motifs with muscles.” Holt's modular theory ...
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This chapter explains the use of modular or motif-based theory to interpret the dynamics of whole food webs. According to Robert Holt, modules are “as motifs with muscles.” Holt's modular theory focuses on the implications of the strength of the interactions on the dynamics and persistence of these units. In this book, the term “module” means all motifs that include interaction strength, whereas the term “motif” represents all possible subsystem connections, including the trivial one-node/species case to the n-node/species cases. Part 2 considers the dynamics of important ecological modules or motifs such as populations, consumer–resource interactions, food chains, and omnivory, while Part 3 uses the logic attained from this modular or motif-based theory in order to elucidate the dynamics of whole food webs. The book argues that ecologists must make a concerted effort to understand how coupling different modules ultimately modifies flux within each individual module.Less

Of Modules, Motifs, and Whole Webs

Kevin S. McCann

Published in print: 2011-12-11

This chapter explains the use of modular or motif-based theory to interpret the dynamics of whole food webs. According to Robert Holt, modules are “as motifs with muscles.” Holt's modular theory focuses on the implications of the strength of the interactions on the dynamics and persistence of these units. In this book, the term “module” means all motifs that include interaction strength, whereas the term “motif” represents all possible subsystem connections, including the trivial one-node/species case to the n-node/species cases. Part 2 considers the dynamics of important ecological modules or motifs such as populations, consumer–resource interactions, food chains, and omnivory, while Part 3 uses the logic attained from this modular or motif-based theory in order to elucidate the dynamics of whole food webs. The book argues that ecologists must make a concerted effort to understand how coupling different modules ultimately modifies flux within each individual module.

This chapter provides a summary of the topics covered by the present volume. The summary serves the purpose of clearly showing how different chapters fit together in a general framework with respect ...
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This chapter provides a summary of the topics covered by the present volume. The summary serves the purpose of clearly showing how different chapters fit together in a general framework with respect to model approaches as well as results obtained. Reading this summary chapter will show readers the different types of community modules that will be analyzed as well as provide a clear impression of the results and insights that presented in this book. Topics discussed include biomass overcompensation, ontogenetic (a)symmetry in energetics, emergent community effects of biomass overcompensation, ontogenetic niche shifts in consumer life history, ontogenetic niche shifts in predator life history, competition between consumers with and without ontogenetic niche shifts, and ontogenetic (a)symmetry in energetics and population dynamics.Less

Summary : A Bird’s-Eye View of Community and Population Effects of Ontogenetic Development

André M. de RoosLennart Persson

Published in print: 2013-01-15

This chapter provides a summary of the topics covered by the present volume. The summary serves the purpose of clearly showing how different chapters fit together in a general framework with respect to model approaches as well as results obtained. Reading this summary chapter will show readers the different types of community modules that will be analyzed as well as provide a clear impression of the results and insights that presented in this book. Topics discussed include biomass overcompensation, ontogenetic (a)symmetry in energetics, emergent community effects of biomass overcompensation, ontogenetic niche shifts in consumer life history, ontogenetic niche shifts in predator life history, competition between consumers with and without ontogenetic niche shifts, and ontogenetic (a)symmetry in energetics and population dynamics.

This chapter investigates the necessary conditions for the biomass in particular size ranges of a population to increase in response to an increase in mortality, and how the overcompensation comes ...
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This chapter investigates the necessary conditions for the biomass in particular size ranges of a population to increase in response to an increase in mortality, and how the overcompensation comes about through a change in the population energetics. Ultimately, this overcompensation in stage-specific biomass solely results from the interplay between mortality and intraspecific, exploitative competition for resources among consumers. As a direct effect, mortality decreases overall density, but indirectly benefits survivors through the relaxation of competition for resources. This change in resource use by the consumer population may lead to biomass overcompensation, even in the absence of any increase in resource productivity.Less

Biomass Overcompensation

André M. de RoosLennart Persson

Published in print: 2013-01-15

This chapter investigates the necessary conditions for the biomass in particular size ranges of a population to increase in response to an increase in mortality, and how the overcompensation comes about through a change in the population energetics. Ultimately, this overcompensation in stage-specific biomass solely results from the interplay between mortality and intraspecific, exploitative competition for resources among consumers. As a direct effect, mortality decreases overall density, but indirectly benefits survivors through the relaxation of competition for resources. This change in resource use by the consumer population may lead to biomass overcompensation, even in the absence of any increase in resource productivity.

This chapter considers the consequences for community structure of ontogenetic diet shifts that involve the use of different resources in different life history stages, whereby these resources are in ...
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This chapter considers the consequences for community structure of ontogenetic diet shifts that involve the use of different resources in different life history stages, whereby these resources are in limited supply and are hence competed for by all individuals foraging on them. It explores the consequences of ontogenetic diet shifts using stage-structured biomass models that account for two basic resources, a stage-structured consumer population, for which we distinguish between juveniles and adults, and up to two unstructured predator populations. The most extended model is therefore closely related to the model analyzed in Chapter 5, except for the inclusion of an additional basic resource. The equations of the full model are summarized and default parameter values are listed.Less

Ontogenetic Niche Shifts

André M. de RoosLennart Persson

Published in print: 2013-01-15

This chapter considers the consequences for community structure of ontogenetic diet shifts that involve the use of different resources in different life history stages, whereby these resources are in limited supply and are hence competed for by all individuals foraging on them. It explores the consequences of ontogenetic diet shifts using stage-structured biomass models that account for two basic resources, a stage-structured consumer population, for which we distinguish between juveniles and adults, and up to two unstructured predator populations. The most extended model is therefore closely related to the model analyzed in Chapter 5, except for the inclusion of an additional basic resource. The equations of the full model are summarized and default parameter values are listed.

The previous two chapters discussed how the size scaling of foraging and metabolic rates affected the dynamics of consumer-resource systems. Using different modeling approaches, it was shown that ...
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The previous two chapters discussed how the size scaling of foraging and metabolic rates affected the dynamics of consumer-resource systems. Using different modeling approaches, it was shown that stage-dependent competitive ability was the main predictor of population dynamics; that is, it largely set the conditions for different types of cycles to occur. This chapter adds another intraspecific interaction on top of the consumer-resource system, namely, cannibalism. It uses a discrete-continuous population-level model based on individual-level net-production energetics to investigate the effects of cannibalism. The focus will be on the effects of cannibalism on population dynamics related to four processes that have been discussed in the literature regarding cannibalism: effects on mortality, competition, energy gain, and the size dependence of interactions.Less

Cannibalism in Size-Structured Systems

André M. de RoosLennart Persson

Published in print: 2013-01-15

The previous two chapters discussed how the size scaling of foraging and metabolic rates affected the dynamics of consumer-resource systems. Using different modeling approaches, it was shown that stage-dependent competitive ability was the main predictor of population dynamics; that is, it largely set the conditions for different types of cycles to occur. This chapter adds another intraspecific interaction on top of the consumer-resource system, namely, cannibalism. It uses a discrete-continuous population-level model based on individual-level net-production energetics to investigate the effects of cannibalism. The focus will be on the effects of cannibalism on population dynamics related to four processes that have been discussed in the literature regarding cannibalism: effects on mortality, competition, energy gain, and the size dependence of interactions.

This chapter examines how nutrient recycling and decomposition affect the dynamics and stability of food webs. It first reviews some of the existing theory on detritus and food web dynamics before ...
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This chapter examines how nutrient recycling and decomposition affect the dynamics and stability of food webs. It first reviews some of the existing theory on detritus and food web dynamics before discussing the basics of a model that takes into account grazing food webs and whole ecosystems. It then describes the N-R-D (nutrient pool, resource, detritus) submodule as well as the full N-C-R-D (nutrient pool, consumer, resource, detritus) model. It also explores how detritus may act to distribute nutrients by considering a model that begets nonequilibrium dynamics. It shows that detritus tends to stabilize consumer–resource interactions relative to the purely community module (no recycling) because the detritus tends to fall out of phase with the resource–nutrient interaction. The addition of a consumer–resource incteraction to the N-R-D module, even in a closed system, eventually can drive overshoot dynamics and destabilization by increased production, coupling, or interaction strength.Less

Adding the Ecosystem

Kevin S. McCann

Published in print: 2011-12-11

This chapter examines how nutrient recycling and decomposition affect the dynamics and stability of food webs. It first reviews some of the existing theory on detritus and food web dynamics before discussing the basics of a model that takes into account grazing food webs and whole ecosystems. It then describes the N-R-D (nutrient pool, resource, detritus) submodule as well as the full N-C-R-D (nutrient pool, consumer, resource, detritus) model. It also explores how detritus may act to distribute nutrients by considering a model that begets nonequilibrium dynamics. It shows that detritus tends to stabilize consumer–resource interactions relative to the purely community module (no recycling) because the detritus tends to fall out of phase with the resource–nutrient interaction. The addition of a consumer–resource incteraction to the N-R-D module, even in a closed system, eventually can drive overshoot dynamics and destabilization by increased production, coupling, or interaction strength.